The purpose of Project 5 is to further understand the signal transduction events in the Fanconi Anemia (FA) pathway. The grant is significant since a molecular understanding of FA may lead to a general understanding of aplastic anemia and cancer susceptibility in the general (non-FA) population. Also, FA is a candidate disease for gene therapy, based on the selective advantage of FA cDNA transduced hematopoietic progenitor cells. Our laboratory has recently determined that the six cloned FA genes (corresponding to subtypes A,C,D2,E,F, and G) interact in a novel signaling pathway, which regulates DNA repair and ultimately regulates normal blood cell production. Disruption of this pathway leads to the common clinical and cellular phenotype observed in FA. Specific Aim 1 for the five year study period will be to study the molecular interaction between the FA pathway and the Ataxia Telangiectasia Protein, ATM. Our preliminary data demonstrate that the FANCD2 protein is monoubiquitinated by the FA protein complex (A/C/E/F/G complex) and phosphorylated by ATM. In Specific Aim 2, we will develop murine models of FA (i.e., ATM/FANCG double knockout mice FANCD2 -/- mice) and will study hematopoiesis and leukemia susceptibility in these mice. In Specific Aim 3, we will use Drosophila genetics to validate various biochemical features of the FA pathway. Through the execution of these three specific aims, we plan extensive interactions with the four other projects in this Program Project and with the flow cytometry core and mouse pathology core.